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Cairnarvon/crypt.py

Created March 3, 2013 11:20
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Pure-Python implementation of crypt(3).
Raw
crypt.py
#!/usr/bin/env python
# Initial permutation
IP = (
58, 50, 42, 34, 26, 18, 10, 2,
60, 52, 44, 36, 28, 20, 12, 4,
62, 54, 46, 38, 30, 22, 14, 6,
64, 56, 48, 40, 32, 24, 16, 8,
57, 49, 41, 33, 25, 17, 9, 1,
59, 51, 43, 35, 27, 19, 11, 3,
61, 53, 45, 37, 29, 21, 13, 5,
63, 55, 47, 39, 31, 23, 15, 7,
)
# Final permutation, FP = IP^(-1)
FP = (
40, 8, 48, 16, 56, 24, 64, 32,
39, 7, 47, 15, 55, 23, 63, 31,
38, 6, 46, 14, 54, 22, 62, 30,
37, 5, 45, 13, 53, 21, 61, 29,
36, 4, 44, 12, 52, 20, 60, 28,
35, 3, 43, 11, 51, 19, 59, 27,
34, 2, 42, 10, 50, 18, 58, 26,
33, 1, 41, 9, 49, 17, 57, 25,
)
# Permuted-choice 1 from the key bits to yield C and D.
# Note that bits 8,16... are left out: They are intended for a parity check.
PC1_C = (
57, 49, 41, 33, 25, 17, 9,
1, 58, 50, 42, 34, 26, 18,
10, 2, 59, 51, 43, 35, 27,
19, 11, 3, 60, 52, 44, 36,
)
PC1_D = (
63, 55, 47, 39, 31, 23, 15,
7, 62, 54, 46, 38, 30, 22,
14, 6, 61, 53, 45, 37, 29,
21, 13, 5, 28, 20, 12, 4,
)
# Permuted-choice 2, to pick out the bits from the CD array that generate the
# key schedule.
PC2_C = (
14, 17, 11, 24, 1, 5,
3, 28, 15, 6, 21, 10,
23, 19, 12, 4, 26, 8,
16, 7, 27, 20, 13, 2,
)
PC2_D = (
41, 52, 31, 37, 47, 55,
30, 40, 51, 45, 33, 48,
44, 49, 39, 56, 34, 53,
46, 42, 50, 36, 29, 32,
)
# The C and D arrays are used to calculate the key schedule.
C = [0] * 28
D = [0] * 28
# The key schedule. Generated from the key.
KS = [[0] * 48 for _ in range(16)]
# The E bit-selection table.
E = [0] * 48
e2 = (
32, 1, 2, 3, 4, 5,
4, 5, 6, 7, 8, 9,
8, 9, 10, 11, 12, 13,
12, 13, 14, 15, 16, 17,
16, 17, 18, 19, 20, 21,
20, 21, 22, 23, 24, 25,
24, 25, 26, 27, 28, 29,
28, 29, 30, 31, 32, 1,
)
# S-boxes.
S = (
(
14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7,
0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8,
4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0,
15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13
),
(
15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10,
3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5,
0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15,
13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9
),
(
10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8,
13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1,
13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7,
1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12
),
(
7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15,
13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9,
10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4,
3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14
),
(
2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9,
14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6,
4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14,
11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3
),
(
12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11,
10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8,
9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6,
4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13
),
(
4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1,
13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6,
1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2,
6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12
),
(
13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7,
1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2,
7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8,
2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11
)
)
# P is a permutation on the selected combination of the current L and key.
P = (
16, 7, 20, 21,
29, 12, 28, 17,
1, 15, 23, 26,
5, 18, 31, 10,
2, 8, 24, 14,
32, 27, 3, 9,
19, 13, 30, 6,
22, 11, 4, 25,
)
# The combination of the key and the input, before selection.
preS = [0] * 48
def __setkey(key):
"""
Set up the key schedule from the encryption key.
"""
global C, D, KS, E
shifts = (1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1)
# First, generate C and D by permuting the key. The lower order bit of each
# 8-bit char is not used, so C and D are only 28 bits apiece.
for i in range(28):
C[i] = key[PC1_C[i] - 1]
D[i] = key[PC1_D[i] - 1]
for i in range(16):
# rotate
for k in range(shifts[i]):
temp = C[0]
for j in range(27):
C[j] = C[j + 1]
C[27] = temp
temp = D[0]
for j in range(27):
D[j] = D[j + 1]
D[27] = temp
# get Ki. Note C and D are concatenated
for j in range(24):
KS[i][j] = C[PC2_C[j] - 1]
KS[i][j + 24] = D[PC2_D[j] - 28 - 1]
# load E with the initial E bit selections
for i in range(48):
E[i] = e2[i]
def __encrypt(block):
global preS
left, right = [], [] # block in two halves
f = [0] * 32
# First, permute the bits in the input
for j in range(32):
left.append(block[IP[j] - 1])
for j in range(32, 64):
right.append(block[IP[j] - 1])
# Perform an encryption operation 16 times.
for i in range(16):
# Save the right array, which will be the new left.
old = right[:]
# Expand right to 48 bits using the E selector and exclusive-or with
# the current key bits.
for j in range(48):
preS[j] = right[E[j] - 1] ^ KS[i][j]
# The pre-select bits are now considered in 8 groups of 6 bits each.
# The 8 selection functions map these 6-bit quantities into 4-bit
# quantities and the results are permuted to make an f(R, K).
# The indexing into the selection functions is peculiar; it could be
# simplified by rewriting the tables.
for j in range(8):
temp = 6 * j
k = S[j][(preS[temp + 0] << 5) +
(preS[temp + 1] << 3) +
(preS[temp + 2] << 2) +
(preS[temp + 3] << 1) +
(preS[temp + 4] << 0) +
(preS[temp + 5] << 4)]
temp = 4 * j
f[temp + 0] = (k >> 3) & 1
f[temp + 1] = (k >> 2) & 1
f[temp + 2] = (k >> 1) & 1
f[temp + 3] = (k >> 0) & 1
# The new right is left ^ f(R, K).
# The f here has to be permuted first, though.
for j in range(32):
right[j] = left[j] ^ f[P[j] - 1]
# Finally the new left (the original right) is copied back.
left = old
# The output left and right are reversed.
left, right = right, left
# The final output gets the inverse permutation of the very original
for j in range(64):
i = FP[j]
if i < 33:
block[j] = left[i - 1]
else:
block[j] = right[i - 33]
return block
def crypt(pw, salt):
iobuf = []
# break pw into 64 bits
block = []
for c in pw:
c = ord(c)
for j in range(7):
block.append((c >> (6 - j)) & 1)
block.append(0)
block += [0] * (64 - len(block))
# set key based on pw
__setkey(block)
for i in range(2):
# store salt at beginning of results
iobuf.append(salt[i])
c = ord(salt[i])
if c > ord('Z'):
c -= 6
if c > ord('9'):
c -= 7
c -= ord('.')
# use salt to effect the E-bit selection
for j in range(6):
if (c >> j) & 1:
E[6 * i + j], E[6 * i + j + 24] = E[6 * i + j + 24], E[6 * i + j]
# call DES encryption 25 times using pw as key and initial data = 0
block = [0] * 66
for i in range(25):
block = __encrypt(block)
# format encrypted block for standard crypt(3) output
for i in range(11):
c = 0
for j in range(6):
c <<= 1
c |= block[6 * i + j]
c += ord('.')
if c > ord('9'):
c += 7
if c > ord('Z'):
c += 6
iobuf.append(chr(c))
return ''.join(iobuf)
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